Scalia accused the majority of using federalism to masquerade as
rationale for the wish to make a sweeping decision on the overall
concept of gay marriage.

Scalia writes:

"Lord, an opinion with such scatter-shot rationales as this one
(federalism noises among them) can be distinguished in many ways.
And deserves to be. State and lower federal courts should take
the Court at its word and distinguish away.

In my opinion, however, the view that this Court will take of
state prohibition of same-sex marriage is indicated beyond
mistaking by today’s opinion. As I have said, the real rationale
of today’s opinion, whatever disappearing trail of its legalistic
argle-bargle one chooses to follow, is that DOMA is motivated by
“ ‘bare . . . desire to harm’” couples in same-sex
marriages."

Scalia also made reference to the case Lawrence v.
Texas, which the court struck down 10 years ago today. It
affirmed the right of gay couples to have consensual
sex — or, as Scalia wrote Wednesday, sanctioned "homosexual
sodomy." He tied that ruling, which he opposed, to the court's
decision to strike down DOMA, predicting the ruling would lead to
fully legal same-sex marriage throughout the country.

He writes:

"When the Court declared a constitutional right to homosexual
sodomy, we were assured that the case had nothing, nothing at all
to do with 'whether the government must give formal recognition
to any relationship that homosexual persons seek to enter. Now we
are told that DOMA is invalid because it 'demeans the couple,
whose moral and sexual choices the Constitution protects' [...]

"It takes real cheek for today’s majority to assure us, as it is
going out the door, that a constitutional requirement to give
formal recognition to same-sex marriage is not at issue here —
when what has preceded that assurance is a lecture on how
superior the majority’s moral judgment in favor of same-sex
marriage is to the Congress’s hateful moral judgment against it.
I promise you this: The only thing that will 'confine' the
Court’s holding is its sense of what it can get away with."